The subject matter disclosed herein relates to dual-energy X-ray imaging.
Non-invasive imaging technologies allow images of the internal structures or features of a patient to be obtained without performing an invasive procedure on the patient. In particular, such non-invasive imaging technologies rely on various physical principles, such as the differential transmission of X-rays through the target volume or the reflection of acoustic waves, to acquire data and to construct images or otherwise represent the observed internal features of the patient.
For example, in computed tomography (CT) and other X-ray-based imaging technologies, X-ray radiation spans a subject of interest, such as a human patient, and a portion of the radiation impacts a detector where the intensity data is collected. In scintillator-based detector systems, a scintillator material generates optical or other low-energy photons when exposed to the X-ray and a photodetector then produces signals representative of the amount or intensity of radiation observed on that portion of the detector. The signals may then be processed to generate an image that may be displayed for review. In CT systems, this X-ray transmission information is collected at various angular positions as a gantry is rotated around a patient to allow volumetric reconstructions to be generated.
In clinical practice it may be desirable to acquire such X-ray transmission data at more than one X-ray energy, or spectrum, as the difference in X-ray transmission at the different energies can be leveraged to generate images corresponding to different tissue types or conveying information related to the spatial material composition within the imaged region. Such approaches, in a computed tomography context, may be characterized as spectral CT, dual-energy CT or multi-energy CT.
As discussed herein, the spectra may be characterized by the maximum operating voltage (kVp) of an X-ray tube used to generate the X-rays, also denoted as the operating voltage level of the X-ray tube. Though such X-ray emissions may be generally described or discussed herein as being at a particular energy level (e.g., referring to the electron beam energy level in a tube with an operating voltage of, for example, 70 kVp, 150 kVp, and so forth), the respective X-ray emissions actually comprise a continuum or spectrum of energies and may, therefore, constitute a polychromatic emission centered at, terminating at, or having a peak strength at, the target energy.
Such multi-energy imaging approaches necessitate being able to separate the signal attributable to different energy spectra or to different regions of a single spectrum, i.e., good energy separation. Current approaches to achieve energy separation all have drawbacks or tradeoffs related to poor separation of the different energy levels or poor synchronicity, i.e., a temporal offset between when corresponding signals for different spectra are acquired, and/or poor radial correspondence or spatial resolution, i.e., the different energy signals may be acquired at radially offset positions from one another using separate emission and/or detection components.
For example, in a “fast kV switching” dual-energy CT context, an X-ray source (e.g., X-ray tube) is rapidly switched between two or more operating voltages (each of which is associated with a different respective X-ray energy spectrum) at each view angle during gantry rotation. Although the projection data at different energy levels are collected consecutively within two views (which may be preferable than a rotate-rotate or dual source scheme in terms of the temporal offset between different energies) the fast kV switching approach still requires interpolation for view registration. This results in azimuthal blur that may limit improvements in spatial resolution.